1. Field of the Invention
The present invention relates to a reflective type liquid crystal display apparatus that is used for a display function of information display systems, office automation equipment, etc. Specifically, the present invention relates to a reflective type liquid crystal display apparatus including a front light for efficiently illuminating a liquid crystal display device without deteriorating the display quality thereof. Such a display apparatus is therefore preferable for use in portable information terminals or equipment for mobile computing. The present invention also relates to portable electric equipment including such a reflective type liquid crystal display apparatus.
2. Description of the Related Art
In general, liquid crystal display apparatus can be divided into two groups: a group of transmissive type liquid crystal display apparatus which display letters, images, etc., by adjusting the amount of transmitted light which is emitted from a particular light source; and a group of reflective type liquid crystal display apparatus which display letters, images, etc., using ambient light.
The transmissive type liquid crystal display apparatus includes a light source such as a fluorescent light, an electroluminescence (EL) device, or the like, placed on the back surface of a liquid crystal device as a planar light source (backlight). On the other hand, the reflective type liquid crystal display apparatus does not require a backlight because it displays images using ambient light. Thus, the reflective type liquid crystal display apparatus enjoys advantages such as light weight, thin shape, low power consumption, etc. Furthermore, in a highly bright environment in which sunlight is incident directly on the display device, the reflective type liquid crystal display apparatus enables a viewer to observe images more clearly, whereas the transmissive type liquid crystal display apparatus exhibits serious deterioration in the visibility of images. Thus, demands for the reflective type liquid crystal display apparatus have been increasing, and such a reflective type device is more likely for application in portable electronic equipment such as portable information terminals or apparatus for mobile computing.
However, it is sometimes impossible for the reflective type liquid crystal display apparatus to provide sufficient display in a dark environment such as nighttime or the like because the reflective type liquid crystal display apparatus uses ambient light for display and the display brightness thereof heavily depends on environmental conditions. Specifically, such a drawback is a major problem in a reflective type liquid crystal display apparatus which uses a color filter for displaying color images or in a reflective type liquid crystal display apparatus which uses polarizing plates.
In order to address such a drawback, it has been proposed to provide an illumination device called a front light for illuminating, in the case of insufficient ambient light, a reflective type liquid crystal device from the front face thereof.
For example, CX. PAL Vol. 40 (Sony Semiconductor News pp. 26-27) describes an example of such a front light. This document discloses a conventional front light including a light guide for converting a light from a light source into planar emission light, and an optical film composed of a polarizing plate and a quarter-wave plate which are combined and placed on the emission surface side of the light guide.
However, the above-described conventional art involves the drawbacks described below.
In general, an electronic information apparatus is covered with a case (a protection element) for protecting a liquid crystal display device. The case is provided with a window through which a viewer observes a display screen. For example, referring to FIG. 11A, in a reflective type liquid crystal display apparatus 450, a window 401a is formed in a size larger than a display area 402 which corresponds to a plurality of pixels formed in the reflective type liquid crystal display device.
The window 401a is designed so that an unobservable display area does not occur (i.e., the entire display area 402 can be seen) even when observed from an oblique direction. This is because peripheral portions 402y of the display area 402 cannot be seen when a viewer 400 observes the display area 402 through the window 401a from an oblique direction (a direction not vertical to the screen) as shown in FIG. 11B. The window 401a is typically formed larger than the display area 402 by about 1 mm in each direction, in consideration of an attachment margin as well as an unobservable display area 402y. 
In a reflective type liquid crystal display apparatus including a front light (an illuminator) for illuminating a reflective type liquid crystal display device, the front light and the liquid crystal display device are covered with a case, and a window is formed in a viewer-side face of the case through which the viewer observes the screen of the liquid crystal display device.
In such a structure, when the size of the light guide is too large relative to the size of the window, electronic equipment becomes large, and the portability thereof may therefore deteriorate. Furthermore, in the case where the size of the light guide of the front light is smaller than the size of the window, light leaks from end faces of the light guide when the light is on, which is observable by the viewer. As a result, display quality of the liquid crystal display apparatus significantly deteriorates.
Furthermore, in the case where an optical film is provided under a lower surface of the light guide (an opposite side to the viewer), especially when an adhesion layer is provided between the light guide and the optical film, light leaks from the end faces of the light guide, end faces of the optical film, and an interface between the adhesion layer and the light guide. As a result, display quality significantly deteriorates.
Yet, CX. PAL Vol. 40 (Sony Semiconductor News pp. 26-27) does not disclose any means of solving such problems.
According to one aspect of the present invention, a reflective type liquid crystal display apparatus includes: a reflective type liquid crystal display device for displaying images by reflecting incident light in such a manner that the incident light is separately controlled for each pixel; a front light positioned at a front face side of the reflective type liquid crystal display device, the front light including a light source and a light guide, wherein light emitted from the light source enters the light guide from an end face thereof near the light source, and the light is output from a large face of the light guide which faces the liquid crystal display device; and a protection member for covering the reflective type liquid crystal display device and the front light, wherein a window is formed in the protection member at a front face side of the front light for a viewer to observe the images displayed on the reflective type liquid crystal display device, wherein, at a side of the front light in which the light source is not provided, a distance between an end face of the window formed in the protection member and an end face of light guide adjacent thereto is determined so that light incident in a direction within a desirable viewing angle range passes through a lower face of the light guide.
In one embodiment of the present invention, the protection member covers an end portion of the light guide such that distance X1 between an end face of the window and an end face of the light guide is within the following range:   0  ≦  X1  ≦            ∑              i        =        1            g        ⁢          xe2x80x83        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    i                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      i                                                        )                                                      )                              )      
(where ti+1 is a thickness of the (i+1)th layer; ni and ni+1 are refractive indices of the i-th layer and the (i+1)th layer, respectively; angle xcex8i is an angle between a direction of light incident on the i-th layer and a direction perpendicular to the front light; the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; and the relationship nixc3x97sin xcex81=ni+1xc3x97sin xcex8i+1 is satisfied); and the front light includes g layers; the adjacent layers have different refractive indices; the g-th layer is adjacent to the light guide; and the (g+1)th layer is the light guide.
In another embodiment of the present invention, when i=1, ni=1.00.
In still another embodiment of the present invention, when i=1, xcex81=80xc2x0.
In still another embodiment of the present invention, the protection member covers an end portion of the light guide such that distance X1 between an end face of the window and an end face of the light guide is within the following range:             ∑              i        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      i                                                        )                                                      )                              )        ≦  X1  ≦            ∑              i        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      i                                                        )                                                      )                              )      
(where ti+1 is a thickness of the (i+1)th layer: ni and ni+1 are refractive indices of the i-th layer and the (i+1)th layer, respectively; angle xcex8i is an angle between a direction of light incident on the i-th layer and a direction perpendicular to the front light; the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; angle xcfx86i is an angle between a direction of light incident on the i-th layer and a direction perpendicular to the front light; the angle xcfx861 in the 1st layer is a perspective angle; and the relationships nixc3x97sin xcex8i=ni+1xc3x97sin xcex8i+1, and nixc3x97sin xcfx86i=ni+1xc3x97sin xcfx86i+1 are satisfied); and the front light includes g layers; the adjacent layers have different refractive indices; the g-th layer is adjacent to the light guide; and the (g+1)th layer is the light guide.
In still another embodiment of the present invention, the perspective angle xcfx861, in the 1st layer (i=1) is smaller than 4xc2x0.
In still another embodiment of the present invention, the front light further includes an optical film positioned on a large face of the light guide which faces the reflective type liquid crystal display device.
In still another embodiment of the present invention, at a side in which the light source is not provided, the protection member covers an end portion of the optical film such that distance X3 between an end face of the window and an end face of the optical film is within the following range:   0  ≦  X3  ≦            ∑              k        =        1            m        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      k                                                        )                                                      )                              )      
(where tk+1 is a thickness of the (k+1)th layer; nk and nk+1 are refractive indices of the k-th layer and the (k+1)th layer, respectively: angle xcex8k is an angle between a direction of light incident on the k-th layer and a direction perpendicular to the front light: the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; and the relationship nkxc3x97sin xcex8k=nk+1xc3x97sin xcex8k+1 is satisfied): and the front light includes m layers; the adjacent layers have different refractive indices; the m-th layer is the light guide; and the (m+1)th layer is the optical film.
In still another embodiment of the present invention, when k=1, ni=1.00.
In still another embodiment of the present invention, when k=1, xcex81=80xc2x0.
In still another embodiment of the present invention, the protection member covers an end portion of the optical film such that distance X3 between an end face of the window and an end face of the optical film is is within the following range:             ∑              k        =        1            m        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      k                                                        )                                                      )                              )        ≦  X3  ≦            ∑              k        =        1            m        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                          90              -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      k                                                        )                                                      )                              )      
(where tk+1 is a thickness of the (k+1)th layer: nk and nk+1 are refractive indices of the k-th layer and the (k+1)th layer, respectively; angle xcex8k is an angle between a direction of light incident on the k-th layer and a direction perpendicular to the front light; the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; angle xcfx86k is an angle between a direction of light incident on the k-th layer and a direction perpendicular to the front light; the angle xcfx861 in the 1st layer is a perspective angle; and the relationships nkxc3x97sin xcex8k=nk+1xc3x97sin xcex8k+1, and nkxc3x97sin xcfx86k=nk+1xc3x97sin xcfx86k+1 are satisfied); and the front light includes m layers; the adjacent layers have different refractive indices; the m-th layer is the light guide; and the (m+1)th layer is the optical film.
In still another embodiment of the present invention, the perspective angle xcfx861 in the 1st layer (k=1) is smaller than 4xc2x0.
In still another embodiment of the present invention, the optical film has an anti-reflection effect.
In still another embodiment of the present invention, the optical film includes a polarizing plate and a quarter-wave plate.
In still another embodiment of the present invention, the optical film includes a polarizing plate, a half-wave plate, and a quarter-wave plate.
According to another aspect of the present invention, portable electronic equipment includes the reflective type liquid crystal display apparatus of claim 1.
According to still another aspect of the present invention, a reflective type liquid crystal display apparatus includes: a reflective type liquid crystal display device for displaying images by reflecting incident light in such a manner that the incident light is separately controlled for each pixel; a front light positioned at a front face side of the reflective type liquid crystal display device, the front light including a light source and a light guide, wherein light emitted from the light source enters the light guide from an end face thereof near the light source, and the light is output from a large face of the light guide which faces the liquid crystal display device; and a protection member for covering the reflective type liquid crystal display device and the front light, wherein a window is formed in the protection member at a front face side of the front light for a viewer to observe the images displayed on the reflective type liquid crystal display device, wherein, at a side of the front light in which the light source is provided, a distance between an end face of the window formed in the protection member and an end face of light guide adjacent thereto is determined so that light which is emitted from the light source and reflected by a lower face of the front light is not observed by the viewer.
In one embodiment of the present invention, the protection member covers an end portion of the light guide such that distance X2 between an end face of the window and an end face of the light guide is within the following range:   0  ≦  X2  ≦            {                        ∑                      i            =            1                    g                ⁢                  (                                    t                              i                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              i                                                        /                                                          n                                                              i                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          i                                                                    )                                                                      )                                              )                    }        +          (                        t                      g            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          g                                                /                                                  n                                                      g                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      g                                                        )                                                      )                              )      
(where ti+1 is a thickness of the (i+1)th layer; ni and ni+1 are refractive indices of the i-th layer and the (i+1)th layer, respectively, angle xcex8i is an angle between a direction of light incident on the i-th layer and a direction perpendicular to the front light; the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; and the relationship nixc3x97sin xcex8i=ni+1xc3x97sin xcex8i+1 is satisfied); and the front light includes g layers; the adjacent layers have different refractive indices: the g-th layer is adjacent to the light guide; and the (g+1)th layer is the light guide.
In another embodiment of the present invention, when i=1, n1=1.00.
In still another embodiment of the present invention, when i=1, xcex81=80xc2x0.
In still another embodiment of the present invention, the protection member covers an end portion of the light guide such that distance X2 between an end face of the window and an end face of the light guide is within the following range:                     ∑                  j          =          1                g            ⁢              (                              t                          i              +              1                                /                      tan            ⁡                          (                                                90                  ⁢                  xc2x0                                -                                                      sin                                          -                      1                                                        ⁡                                      (                                                                  (                                                                              n                            i                                                    /                                                      n                                                          i                              +                              1                                                                                                      )                                            ⁢                      X                      ⁢                                              xe2x80x83                                            ⁢                      sin                      ⁢                                              xe2x80x83                                            ⁢                                              ϕ                        i                                                              )                                                              )                                      )              +          (                        t                      g            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          g                                                /                                                  n                                                      g                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      g                                                        )                                                      )                              )        ≦  X2  ≦            {                        ∑                      i            =            1                    g                ⁢                  (                                    t                              i                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              i                                                        /                                                          n                                                              i                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          i                                                                    )                                                                      )                                              )                    }        +          (                        t                      g            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          g                                                /                                                  n                                                      g                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      g                                                        )                                                      )                              )      
(where ti+1 is a thickness of the (i+1)th layer; ni and ni+1 are refractive indices of the i-th layer and the (i+1)th layer, respectively; angle xcex8i is an angle between a direction of light incident on the L-th layer and a direction perpendicular to the front light; the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; angle xcfx86i is an angle between a direction of light incident on the i-th layer and a direction perpendicular to the front light: the angle xcfx861 in the 1st layer is a perspective angle: and the relationships nixc3x97sin xcex8i=ni+1xc3x97sin xcex8i+1, and nixc3x97sin xcfx86i=ni+1xc3x97sin xcfx86i+1 are satisfied); and the front light includes g layers; the adjacent layers have different refractive indices; the g-th layer is adjacent to the light guide; and the (g+1)th layer is the light guide.
In still another embodiment of the present invention, the perspective angle xcfx861 in the 1st layer (i=1) is smaller than 4xc2x0.
In still another embodiment of the present invention, the front light further includes an optical film positioned on a large face of the light guide which faces the reflective type liquid crystal display device.
In still another embodiment of the present invention, at a side in which the light source is provided, the protection member covers an end portion of the optical film such that distance X4 between an end face of the window and an end face of the optical film is within the following range:   0  ≦  X4  ≦            {                        ∑                      k            =            1                    m                ⁢                  (                                    t                              k                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              k                                                        /                                                          n                                                              k                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          k                                                                    )                                                                      )                                              )                    }        +          (                        t          m                /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                                                      m                            -                            1                                                                          /                                                  n                          m                                                                    )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                                              m                        -                        1                                                                              )                                                      )                              )        +          (                        t                      m            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          m                                                /                                                  n                                                      m                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      m                                                        )                                                      )                              )      
(where tk+1 is a thickness of the (k+1)th layer; nk and nk+1 are refractive indices of the k-th layer and the (k+1)th layer, respectively; angle xcex8k is an angle between a direction of light incident on the k-th layer and a direction perpendicular to the front light: the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; and the relationship nkxc3x97sin xcex8k=nk+1xc3x97sin xcex8k+1 is satisfied); and the front light includes m layers; the adjacent layers have different refractive indices; the m-th layer is the light guide: and the (m+1)th layer is the optical film.
In still another embodiment of the present invention, when k=1, n1=1.00.
In still another embodiment of the present invention, when k=1, xcex81=80xc2x0.
In still another embodiment of the present invention, the protection member covers an end portion of the optical film such that distance X4 between an end face of the window and an end face of the optical film is within the following range:                     ∑                  k          =          1                m            ⁢              (                              t                          k              +              1                                /                      tan            ⁡                          (                                                90                  ⁢                  xc2x0                                -                                                      sin                                          -                      1                                                        ⁡                                      (                                                                  (                                                                              n                            k                                                    /                                                      n                                                          k                              +                              1                                                                                                      )                                            ⁢                      X                      ⁢                                              xe2x80x83                                            ⁢                      sin                      ⁢                                              xe2x80x83                                            ⁢                                              ϕ                        k                                                              )                                                              )                                      )              +          (                        t          m                /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                                                      m                            -                            1                                                                          /                                                  n                          m                                                                    )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                                              m                        -                        1                                                                              )                                                      )                              )        +          (                        t                      m            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          m                                                /                                                  n                                                      m                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      m                                                        )                                                      )                              )        ≦  X4  ≦            {                        ∑                      k            =            1                    m                ⁢                  (                                    t                              k                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              k                                                        /                                                          n                                                              k                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          k                                                                    )                                                                      )                                              )                    }        +          (                        t          m                /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                                                      m                            -                            1                                                                          /                                                  n                          m                                                                    )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                                              m                        -                        1                                                                              )                                                      )                              )        +          (                        t                      m            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          m                                                /                                                  n                                                      m                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      m                                                        )                                                      )                              )      
(where tk+1 is a thickness of the (k+1)th layer: nk and nk+1 are refractive indices of the k-th layer and the (k+1)th layer, respectively: angle xcex8k is an angle between a direction of light incident on the k-th layer and a direction perpendicular to the front light; the angle xcex81 in the 1st layer is a maximum angle within a desirable viewing angle range; angle xcfx86k is an angle between a direction of light incident on the k-th layer and a direction perpendicular to the front light; the angle xcfx861 in the 1st layer is a perspective angle; and the relationships nkxc3x97sin xcex8k=nk+1xc3x97sin xcex8k+1, and nkxc3x97sin xcfx86k=nk+1xc3x97sin xcfx86k+1 are satisfied); and the front light includes m layers; the adjacent layers have different refractive indices; the m- th layer is the light guide; and the (m+1)th layer is the optical film.
In still another embodiment of the present invention, the perspective angle in the 1st layer (k=1) is smaller than 4xc2x0.
In still another embodiment of the present invention, the optical film has an anti-reflection effect.
In still another embodiment of the present invention, the optical film includes a polarizing plate and a quarter-wave plate.
In still another embodiment of the present invention, the optical film includes a polarizing plate, a half-wave plate, and a quarter-wave plate.
According to still another aspect of the present invention, portable electronic equipment includes the reflective type liquid crystal display apparatus of claim 17.
Hereinafter, the functions of the present invention will be described.
As described above, window 401a is provided in a viewer""s side face of a protection member (case) that protects a liquid crystal display device such that an entire display area can be seen even from an oblique direction. However, when the area of the front face of the light guide is smaller than the area of the window 401a, light leaks from peripheral end faces of the light guide, resulting in significant deterioration of the display quality. In order to address such a drawback, a distance X1 (FIG. 1B) between an end face of the light guide and an end face of the window corresponding thereto is set in a range of 0xe2x89xa6X1, so that the peripheral portion of the light guide is covered with a case. In the case where the display area of the liquid crystal display device is small, the distance X1 may also be small. In this case, the end face of the window and the end face of the light guide are observed substantially in the same viewing direction. When the end face of the light guide is located outside the end face of the window, i.e., 0xe2x89xa6X1, light leakage from the end faces of the light guide does not occur.
A typical liquid crystal display device has a viewing angle range up to about 80xc2x0 from a direction perpendicular to a screen of the liquid crystal display device (angle 0xc2x0). Thus, the light guide may be designed in a size such that the viewing angle range up to about 80xc2x0 is considered, and thus it is not necessary to design the light guide larger than such a size.
The xe2x80x9cviewing angle rangexe2x80x9d of the liquid crystal display device used herein represents a range in which displayed images can be normally seen, excluding a case where a viewer cannot correctly recognize displayed images. Outside the viewing angle range, a black displayed image may appear whitish, or gray-scale inversion may occur, resulting in the deterioration in the contrast or the inversion of the contrast.
As described above, a large-size light guide results in a large-size electronic equipment, whereby portability of the electronic equipment may be reduced. In the present invention, for the purpose of avoiding such a drawback, at a side of a light guide in which a light source is not provided, an end portion of the light guide is covered with a case so that the distance X1 between the end face of the light guide and the end face of the window is within the following range:   0  ≦  X1  ≦            ∑              j        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      i                                                        )                                                      )                              )      
(where, in an air layer of the window (i=1), n1=1.00 and xcex81=80xc2x0). With such an arrangement, light leakage from the end faces of the light guide and the unnecessary reflected light can be prevented over the viewing angle range from 0xc2x0 (lower limit) to 80xc2x0 (upper limit) without spoiling the portability of the liquid crystal display apparatus. Thus, such a liquid crystal display apparatus can be applied to a large-size screen which requires a large viewing angle range, as well as a small-size screen which does not require a large viewing angle range. Furthermore, such a liquid crystal display apparatus is suitable for use in a small-size electronic information apparatus of low power consumption.
An observable area for the viewer should be considered in order to prevent light leakage from the light guide. For example, as shown in FIG. 8, in the case where the viewer observes the center of a 2xe2x80x3 reflective type liquid crystal display device (panel 800) in a direction substantially perpendicular to the panel 800 from a position which is 300 mm away from the panel 800, an area corresponding to an angle of 3.87xc2x0 (about 4xc2x0) in the horizontal direction and an angle of 2.91xc2x0 (about 3xc2x0) in the vertical direction can be observed.
Therefore, in the case where the light guide is provided in front of the liquid crystal display device, the light guide is positioned so as to cover the entire area corresponding to a perspective angle, whereby light leakage from the end face of the light guide can be prevented from reaching the viewer""s eye. For example, in the case of employing a 2xe2x80x3 reflective type liquid crystal display device, the light guide is designed and positioned so as to cover the entire area corresponding to a perspective angle of about 3xc2x0, whereby light leakage toward the viewer can be prevented. More preferably, an area corresponding to a perspective angle of about 4xc2x0 is considered. In the case of employing a 2xe2x80x3 or greater reflective type liquid crystal display device, the perspective angle becomes larger, and an area corresponding there to also becomes larger. In such a case, it is preferable that the light guide is designed and positioned, in consideration of a viewing angle characteristic of the liquid crystal display device, so as to cover an area corresponding to a viewing angle range up to about 80xc2x0 or smaller. Thus, in the present invention, at the side in which the light source is not provided, it is preferable that the end portion of the light guide is covered with the case so that distance X1 between the end face of the window and the end face of the light guide is within the following range:             ∑              i        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      i                                                        )                                                      )                              )        ≦  X1  ≦            ∑              i        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      i                                                        )                                                      )                              )      
(where, in the air layer of the window (i=1), perspective angle xcfx861 is smaller than 4xc2x0). With such an arrangement, even in the case of employing a front light for illuminating a small-size liquid crystal display device, light leakage is prevented, and the display quality therefore improves.
Furthermore, according to a viewing angle range required by the liquid crystal display device, at the side in which the light source is not provided, it is preferable that the case covers the end portion of the light guide so that distance X1 between the end face of the window and the end face of the light guide is within the following range:             ∑              i        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      i                                                        )                                                      )                              )        ≦  X1  ≦            ∑              i        =        1            g        ⁢          (                        t                      i            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          i                                                /                                                  n                                                      i                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      i                                                        )                                                      )                              )      
(where, in the air layer of the window (i=1), xcfx861 is a required perspective angle). With such an arrangement, light leakage can be prevented in accordance with a viewing angle characteristic of the liquid crystal display device, and the display quality therefore improves.
On the other hand, at a side in which the light source is provided, relative to the sides in which the light source is not provided, the intensity of light from the light source is greater, and the light emitted from the light source and reflected by the lower face of the light guide should be prevented from reaching the viewer""s eye.
For example, assume an exemplary arrangement in which a touch panel 908, which serves as an input/output device, is provided at the viewer side of the light guide 907 as shown in FIG. 9A. At a side in which the light source 909 is provided (light source side), light incident in the direction of maximum viewing angle xcex81 (light introduced from an air layer 901 (i=1)) travels through a PET film 902, a transparent electrode 903, an air layer 904, a transparent electrode 905, a glass substrate 906, and a light guide 907, and reaches the lower face of the light guide 907 (route R1). The traveling light is refracted by respective interfaces between adjacent layers according to Snell""s law. Thus, while traveling from the upper face of the PET film 902 to the lower face of the light guide 907 which is provided as the (g+1)th layer (7th layer in this example), the light shifts by distance X1 in the horizontal direction. (It should be noted that the front light herein includes g layers.) As shown in FIG. 6A, at a side in which the light source is not provided, the distance between the end face of the window and the end face of the light guide 607 is only required to be larger than X1. For reference, distance X1 is shown in FIG. 9A. As shown in FIG. 9A, at a side in which the light source 909 is provided, in order to prevent light which is emitted from the light source 909 and then reflected by the lower face of the light guide 907 from traveling through route R1 to reach the viewer""s eye, distance X2 between the end face of the case 900 and the end face of the light guide 907 needs to include distance xcex1 in addition to distance X1. Since a portion of the light emitted from the light source 909 is reflected by the lower face of the light guide 907 as shown in FIG. 9B (a partially enlarged view of FIG. 9A), distance a is determined in consideration of angle xcex87, the thickness t7 of the light guide 907, and the refractive index of the light guide 907. Thus, in the present invention, at the light source side, it is preferable that an end portion of the light guide is covered with the case so that distance X2 between the end face of the window and the end face of the light guide is within the following range:   0  ≦  X2  ≦            {                        ∑                      i            =            1                    g                ⁢                  (                                    t                              i                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              i                                                        /                                                          n                                                              i                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                                                  sin                          i                                                                    )                                                                      )                                              )                    }        +          (                        t                      g            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          g                                                /                                                  n                                                      g                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      g                                                        )                                                      )                              )      
With such an arrangement, in a viewing angle range from 0xc2x0 (lower limit) to preferably 80xc2x0 (upper limit), light leakage from the end face of the light guide is prevented, and the light emitted from the light source and then reflected by the lower face of the light guide is prevented from reaching the viewer s eye, without spoiling the portability of the liquid crystal display apparatus.
Furthermore, also at the light source side, it is preferable that distance X2 between the end face of the window of the case and the end face of the light guide is set in consideration of a length corresponding to prospective angles of the panel as described above (e.g., in a 2xe2x80x3 reflective type liquid crystal display device, about 3xc2x0 in the vertical direction, and about 4xc2x0 in the horizontal direction).
For example, it is preferable that the case covers the end portion of the light guide so that distance X2 between the end face of the window and the end face of the light guide is within the following range:                     ∑                  j          =          1                g            ⁢              (                              t                          i              +              1                                /                      tan            ⁡                          (                                                90                  ⁢                  xc2x0                                -                                                      sin                                          -                      1                                                        ⁡                                      (                                                                  (                                                                              n                            i                                                    /                                                      n                                                          i                              +                              1                                                                                                      )                                            ⁢                      X                      ⁢                                              xe2x80x83                                            ⁢                      sin                      ⁢                                              xe2x80x83                                            ⁢                                              ϕ                        i                                                              )                                                              )                                      )              +          (                        t                      g            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          g                                                /                                                  n                                                      g                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      g                                                        )                                                      )                              )        ≦  X2  ≦            {                        ∑                      i            =            1                    g                ⁢                  (                                    t                              i                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              i                                                        /                                                          n                                                              i                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          i                                                                    )                                                                      )                                              )                    }        +          (                        t                      g            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          g                                                /                                                  n                                                      g                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      g                                                        )                                                      )                              )      
(where, in the air layer of the window (i=1), xcfx861 is a required perspective angle). With such an arrangement, light leakage can be prevented in accordance with a viewing angle characteristic of the liquid crystal display device, and the display quality therefore improves.
Alternatively, in the case where an optical film is provided on a lower face of the light guide, light leaks from peripheral end faces of the optical film. Thus, it is preferable that the end faces of the optical film is covered with the case so that, at the side in which the light source is not provided as shown in FIG. 7, distance X3 between the end face of the window and the end face of the optical film is within the following range:   0  ≦  X3  ≦            ∑              k        =        1            m        ⁢          xe2x80x83        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      k                                                        )                                                      )                              )      
(where, in the air layer of the window (k=1), n1=1.00, xcex81 is within a desirable viewing angle range (preferably 80xc2x0)).
In such a case, at the side in which the light source is not provided, considering an area corresponding to a particular perspective angle (with respect to the end face of the window), it is also preferable that the end portion of the optical film is covered with the case so that distance X3 between the end face of the window and the end face of the optical film is within the following range:             ∑              k        =        1            m        ⁢          xe2x80x83        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      k                                                        )                                                      )                              )        ≦  X3  ≦            ∑              k        =        1            m        ⁢          xe2x80x83        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      k                                                        )                                                      )                              )      
(where, in the air layer of the window (k=1), xcfx861 is a desirable perspective angle).
Furthermore, it is preferable that, at the side in which the light source is not provided, the end portion of the optical film is covered with the case so that distance X3 between the end face of the window and the end face of the optical film is set, in accordance with a viewing angle range required for the liquid crystal display device, to be within the following range:             ∑              k        =        1            m        ⁢          xe2x80x83        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      k                                                        )                                                      )                              )        ≦  X3  ≦            ∑              k        =        1            m        ⁢          xe2x80x83        ⁢          (                        t                      k            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          k                                                /                                                  n                                                      k                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      k                                                        )                                                      )                              )      
(where, in the air layer of the window (k=1), xcfx861 is a required perspective angle).
Furthermore, also in the case where an optical film is provided on the lower face of the light guide, at the light source side, relative to the side in which the light source is not provided, the intensity of light from the light source is greater, and the light emitted from the light source and then reflected by the lower face of the light guide should be prevented from reaching the viewer""s eye.
For example, assume an exemplary arrangement in which a touch panel 1010, which serves as an input/output device, is provided at the viewer side of the light guide 1007 as shown in FIG. 10A. At a side in which the light source 1011 is provided (light source side), light incident in the direction of maximum viewing angle xcex81 (light introduced from an air layer 1001 (k=1)) travels through a PET film 1002, a transparent electrode 1003, an air layer 1004, a transparent electrode 1005, a glass substrate 1006, a light guide 1007, and an optical film 1008, and reaches the lower face of the optical film 1008 (route R2). The traveling light is refracted by respective interfaces between adjacent layers according to Snell""s law. Thus, while traveling from the upper face of the PET film 1002 to the lower face of the light guide 1007 which is provided as the (m+1)th layer (8th layer in this example), the light shifts by distance X3 in the horizontal direction. (It should be noted that the front light herein includes layers.) As shown in FIG. 7, at a side in which a light source is not provided, a distance between an end face of the case and an end face of the optical film 708 is only required to be larger than X3. As shown in FIG. 10A, at a side in which a light source 1011 is provided, in order to prevent light which is emitted from the light source 1011 and reflected by the lower surface of the optical film 1008 from traveling through route R2 to reach the viewer""s eye, distance X4 between the end face of the window formed in the case 1000 and the end face of the optical film 1008 needs to include distance xcex2 in addition to distance X3. Since a portion of the light emitted from the light source 1011 is reflected by the lower face of the optical film 1008 as shown in FIG. 10B (a partially enlarged view of FIG. 10A), distance xcex2 is determined in consideration of angle xcex87, angle xcex88, the thicknesses t6 and t7 of the light guide 1007 and the optical film 1008, and the refractive indices of the light guide 1007 and the optical film 1008. Thus, in the present invention, at the light source side, it is preferable that an end portion of the optical film is covered with the case so that distance X4 between the end face of the window and the end face of the optical film is within the following range:   0  ≦  X4  ≦            {                        ∑                      k            =            1                    m                ⁢                  xe2x80x83                ⁢                  (                                    t                              k                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              k                                                        /                                                          n                                                              k                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          k                                                                    )                                                                      )                                              )                    }        +          (                        t          m                /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                                                      m                            -                            1                                                                          /                                                  n                          m                                                                    )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                                              m                        -                        1                                                                              )                                                      )                              )        +          (                        t                      m            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          m                                                /                                                  n                                                      m                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      m                                                        )                                                      )                              )      
(where, in the air layer of the window (k=1), xcfx861 is a required perspective angle). With such an arrangement, in a viewing angle range from 0xc2x0 (lower limit) to preferably 80xc2x0 (upper limit), light reflection which occurs in a direction of the thickness of the optical film, and light reflection by the optical film which occurs around the optical film due to insufficient compensation of a phase by the optical film, can be prevented.
Furthermore, also at the light source side, it is preferable that distance X3 between the end face of the window of the case and the end face of the optical film is set in consideration of a length corresponding to prospective angles of the panel as described above (e.g., in a 2xe2x80x3 reflective type liquid crystal display device, about 3xc2x0 in the vertical direction, and about 4xc2x0 in the horizontal direction).
For example, it is preferable that, at the side in which the light source is provided, the end portion of the optical film is covered with the case so that distance X4 between the end face of the window and the end face of the optical film is set, in accordance with a viewing angle range required for the liquid crystal display device, to be within the following range:                     ∑                  k          =          1                m            ⁢              xe2x80x83            ⁢              (                              t                          k              +              1                                /                      tan            ⁡                          (                                                90                  ⁢                  xc2x0                                -                                                      sin                                          -                      1                                                        ⁡                                      (                                                                  (                                                                              n                            k                                                    /                                                      n                                                          k                              +                              1                                                                                                      )                                            ⁢                      X                      ⁢                                              xe2x80x83                                            ⁢                      sin                      ⁢                                              xe2x80x83                                            ⁢                                              ϕ                        k                                                              )                                                              )                                      )              +          (                        t          m                /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                                                      m                            -                            1                                                                          /                                                  n                          m                                                                    )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                                              m                        -                        1                                                                              )                                                      )                              )        +          (                        t                      m            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          m                                                /                                                  n                                                      m                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          ϕ                      m                                                        )                                                      )                              )        ≦  X4  ≤            {                        ∑                      k            =            1                    m                ⁢                  xe2x80x83                ⁢                  (                                    t                              k                +                1                                      /                          tan              ⁡                              (                                                      90                    ⁢                    xc2x0                                    -                                                            sin                                              -                        1                                                              ⁡                                          (                                                                        (                                                                                    n                              k                                                        /                                                          n                                                              k                                +                                1                                                                                                              )                                                ⁢                        X                        ⁢                                                  xe2x80x83                                                ⁢                        sin                        ⁢                                                  xe2x80x83                                                ⁢                                                  θ                          k                                                                    )                                                                      )                                              )                    }        +          (                        t          m                /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                                                      m                            -                            1                                                                          /                                                  n                          m                                                                    )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                                              m                        -                        1                                                                              )                                                      )                              )        +          (                        t                      m            +            1                          /                  tan          ⁡                      (                                          90                ⁢                xc2x0                            -                                                sin                                      -                    1                                                  ⁡                                  (                                                            (                                                                        n                          m                                                /                                                  n                                                      m                            +                            1                                                                                              )                                        ⁢                    X                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          θ                      m                                                        )                                                      )                              )      
(where, in the air layer of the window (k=1), xcfx861 is a required perspective angle).
In the case where a film having an anti-reflection effect is employed as the optical film, interference between light emitted from the light source and light reflected by an emission surface of the light guide (a large face of the light guide which faces the liquid crystal display device) can be prevented.
In the case where a film composed of a polarizing plate and a quarter-wave plate is employed as the optical film, unnecessary reflection light reflected by the quarter-wave plate or by a surface of a counter (upper) glass substrate of the liquid crystal display device is removed, whereby contrast deterioration can be prevented.
Alternatively, in the case where a film composed of a polarizing plate, a half-wave plate, and a quarter-wave plate is employed as the optical film, the tolerance of the phase delay with respect to the wavelength of the light is compensated for, whereby a circularly polarized state of light can be maintained. As a result, unnecessary reflection light reflected by the quarter-wave plate or by a surface of a counter glass substrate of the liquid crystal display device can be further prevented.
In the specification of the present invention, light incident in the direction of maximum viewing angle is considered. The route of the incident light (for example, route R1 of FIGS. 9 or route R2 of FIG. 10) is identical to a route of light leaking from the reflection surface to the viewer""s eye, although a direction of travelling light is inversive. Thus, it is apparent to those skilled in the art that the distance between the end face of the light guide and the end face of the window of the case or the distance between the end face of the optical film and the end face of the window of the case can be determined based on the route of the incident light so that the light lea)age through the same route can be prevented.
Thus, the invention described herein makes possible the advantage of providing a reflective type liquid crystal display apparatus and a portable electric device in which light leakage from (nd faces of a light guide or an optical film is prevented, without spoiling the portability of the apparatus and the: equipment, thereby increasing display quality.
This and other advantages; of the present invention will become apparent to those skilled in the art upon reading and understanding the. following detailed description with reference to the accompanying figures.